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The Sap is Rising!

Early March 2016

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Resources for extending the learning

Note:  Although many of you may still be receiving snow, spring IS coming.  Spring rolls across different parts of the provinces at different times and so we may mention some happenings a little early for the benefit of our southern-most readers. Officially spring arrives in the Northern Hemisphere on March 20 (Vernal Equinox).  Its a great reason to have a celebration!

Featured Event:  The Sap is Rising! 

Nothing seems to unify Canadians around spring in the outdoors more than maple syrup season, which by mid-month or sooner should be full swing in many parts of Ontario and Eastern Canada. 

Maple syrup was first collected by Native Americans and has been appreciated for a long time:

"There is in some parts of New England a kind of tree...whose juice that weeps out of its incision, if it be permitted slowly to exhale away the excess moisture, doth congeal into a sweet and saccharine substance."

Robert Boyle  Philosophical Works (1663)

But how does it work?  Why does sap “rise” at this particular time of year in this particular kind of tree?  To answer this question, we first must review the parts of a tree, in particular the xylem and the phloem.  The phloem is a thin layer of living cells just under the bark that carry sugars down from the leaves to the rest of the tree.  The xylem is a wider band of sapwood just inside the cambium that carries water, nitrogen and minerals up the tree, pulled along by the gentle tug of evaporation as water leaves the leaf pores.

But two things are very different in the spring:  it’s the xylem that contains the sugary sap, not the phloem, and there is no way, with the leaves missing, to ‘pull’ it up the trunk.  In addition, root pressure is not involved – pieces of living Sugar Maple stem by themselves, standing in water, can be made to create sap flow.

What does happen is linked directly to this specific time of year, when nights fall below freezing and days warm above it.  Take away either of those conditions, and sap does not rise.  What happens is this.  First, in the fall, sugars are transported down into the stems and converted to starch.  In the spring, during the warm days, living cells convert that starch into sugar.  They also generate carbon dioxide gas.  This gas diffuses into the xylem.  As the temperature cools, the gas dissolves, lowering the pressure and pulling the sugary water from the living cells into xylem.  This water is replaced from adjacent cells, which form a conveyor belt for water down to the roots.  As night comes and the temperature drops further, water freezes along the inside walls of the xylem and in between its cells.  The remaining gas is compressed and locked in this ice.  Suction is created, which draws water from the soil into the roots.  With morning, things warm, the gases expand and force the now liquid sap out of the trunk or stem and into the tap.  As the day cools in the afternoon, the process repeats itself.  For more details, go here or here.  The process stops when the temperature remains above freezing and the buds begin to open.

Only a few trees besides Sugar Maples contain the correct cell structure to produce this kind of temperature-related pressure, and include Butternut.  If you’re from the northwest and feel like you’ve missed out on a childhood tradition, pout not -- syrup can also be made from birch trees, but the sap flow comes later in Spring and is dependent on root pressure.  Make your own!

Red Squirrels discovered this process long before we did.  They will nip at a twig to start the flow, then go away for a day or so to allow some water to evaporate and the sugars condense before coming back to consume the thicker sap.  It may have been observation of this behaviour by indigenous peoples that led to their development of the syrup-making process. 

 Related lesson plans and resources can be found here

Other Happenings:

  • March is a month of weather extremes.  Keep track of temperature highs and lows, and compare the amount of snow received to the amount of rain (1 cm of snow is roughly equivalent to 1 mm of rain).   Temperatures this month can sometimes range over 50oC. Test out the folk wisdom that if March “comes in like a lion”, it “goes out like a lamb”, and vice versa.
  • The birds are returning, led by American Robins and male Red-winged Blackbirds(female).  Not only mark the first Red-wing, but check out where they are and what they do.  Do they go straight to the cattails?  When do males begin to call?  Where do they go in bad weather?
  • Migrating Robins, perhaps taking advantage of the generally warmer winter, have already been seen around the western end of Lake Ontario, in spite of the cold, snowy weather that may delay their general push into Canada.   New arrivals are brighter and perkier than any overwintering birds (there’s a flock in Ottawa -- what were they thinking?), but when do you know that your Robins have arrived?  The best way is to listen for their breeding call, which males will only use to establish and hold their territories, often early in the morning.  Of six different Robin calls, only two are territorial.  Report the first Robin you hear to the Journey North website.
  • American Crows are already pairing and searching out nesting sites.  Males will fluff up their body feathers and bow repeatedly to the female.  Also keep an eye out for flying pairs, and stick carrying.  Do you have any pairs around your school?  Nests are generally built high up in evergreen trees.
  • The Snowy Owl irruption continues.  I have personally seen one, and this eBird map gives their distribution for this winter.  The density of owls is unclear at this time, as is the ultimate cause.  This is the third irruption in four years, and while another good lemming summer probably fuelled this migration, why it’s happening so frequently, and whether it is good for either the lemmings or the owls in the long run, is not known.
  • One of the first smells of spring (and much better smelling than skunk) comes from Balsam Poplar buds, where protective resin is softening in the warming sun.  Find some, pinch the buds gently, then smell your fingers.  Red and Silver Maples will also begin flowering shortly.
  • Taking up where his grey cousins left off, the male Red Squirrel can be seen chasing females through the trees.  Chipmunks may also pop up, shaking off the effects of their long, on-again off-again, winter’s nap.  Food is not the issue.  Mating is.
  • Ice out, another rite of spring linked to biodiversity, will occur sometime during March on local lakes, ponds and streams.  Mark the date of your local water body for future reference, and report the information to IceWatch.
  • The moon, Mars and Saturn group together the morning of the 1st, while the Earth is between the sun and Jupiter the evening of the 7th.  The two planets are at their closest point for the year, so Jupiter is quite bright, and up all night.
  • On March 8th a new supermoon occurs as the moon passes close to the Earth, together with a total solar eclipse for parts of Asia and the Pacific.